1. Field of the Invention
The present invention relates to a method and an apparatus for recording video data with compressed bandwidth, such as video signals and sound signals, on storage media and for reproducing and transmitting the video data in response to subscribers' request.
2. Prior Art
Recent rapid progress of compression technologies (i.e. high efficient coding technologies) of video signals and sound signals, development of international standardization of MPEG and others, expansion of storage capacity of storage media, and popularization of digital communication service represented by ISDN, are almost realizing the data base service of moving picture information using the digital communication network. This moving picture information service is capable of request-type service, interactive service or the like, which has not ever been realized by the conventional terrestrial broadcasting and satellite broadcasting services. Therefore, many research and development activities have been carrying out for realization of this kind of service.
It is, however, predicted that one of problems will derive from occupation of a storage medium by one user during service of moving picture information which normally has a length of several tens seconds to several hours a program. A key to the commercial base construction of such kind of system will depend on capability of allowing numerous users to share the storage media simultaneously. Furthermore, the response of the system will need to be quick enough to respond each request from users within an allowable time. For these reasons, the technologies for multiple access to the storage media will be mandatory.
To realize the multiple access, one conventional method proposes to divide moving picture information, such as video signals, into a plurality of blocks, relocate these divided blocks cyclically in a predetermined format, record them onto a disk with a plurality of heads, and reproduce a plurality of video signals having time phases different from each other. (Refer to W. D. Sincoskie "System architecture for a large scale video on demand service" Computer Networks and ISDN System 22 (1991) 155-182) According to this conventional method, the near video on demand type video service will be feasible at relatively low cost and an access time required from request to reception of video service will be shortened within an acceptable time.
However, this conventional recording/reproducing method is disadvantageous in that a special disk equipped with a plurality of recording/reproducing heads needs to be newly developed as a recording medium. This will result in cost increase of the storage medium. Furthermore, construction of interleave depends on the structure of the heads. Therefore, there is no flexibility of freely setting the number of phases to be reproduced simultaneously; i.e. the service interval of video signals. Although the read out video signals of each phase are smoothed and transmitted as a serial signal, the process of smoothing the video signals in this conventional system will be very difficult since the extracting cycle of video signals is not constant. Still further, the start point of a video signal which newly become reproducible is undesirably advanced with respect to the end point of the video signal in each phase. This results in capacity increase of the memory used for the smoothing process. Moreover, time administration will become complicated in controlling the signals streaming on the transmission line.